The goal of this project is to define mechanisms underlying the activation of a single, defined, oncogenic ras family member in cancers of specific organs and tissue. Examples of this specificity include the observations that in human bladder cancer, the activated ras family member is always H-ras, whereas only K-ras activation is found in pancreatic cancer. For reasons of their unique utilities, several rat mammary carcinogenesis models will be used to accomplish the goal of this proposal. For example, rat mammary carcinomas chemically induced by NMU (N-nitrosomethylurea) only have activated H-ras and never have activated K-ras. Based on preliminary data demonstrating that K-vs. H- ras specificity lies in the Ras protein itself, Aim 1 will test the hypothesis that subtle differences in the carboxyl end of the Ras proteins (H- or K-Ras) modify Ras membrane localization, leading to tumor-type specificity. Experimental approaches for this aim include: Ras domain exchanges between H-and K-Ras, Ras-Raf interaction studies, and H- vs. K-Ras immunogold electron microscopic membrane localization studies. In Aim 2, another aspect of ras specificity will be studied using transgenic rats overexpressing wild type H- vs. K-ras. Preliminary data showing that overexpression of wild-type H-ras, but not K-ras, can inhibit NMU-induced mammary carcinoma development will be extended and mechanistically investigated. The differential activation of the H-ras transgene versus the endogenous H-ras gene will also be explored. Aim 3 will follow up preliminary data demonstrating that expression of wild- type H-ras, but not K-ras, driven by a viral MMLV promoter in in situ mammary cells induces mammary carcinomas. This is in contrast to the observation that overexpression of wild-type H-ras does not result in the induction of mammary carcinomas when driven by its own promoter. A hypothesis suggesting that disregulated gene expression is important in wild-type ras-induced carcinogenesis will be investigated. Data generated in this project will provide: insight into the role of ras specificity in the etiology of cancer (approximately 40 percent of human cancers have activated ras), and knowledge for the development of drugs that specifically target single members of the ras family.